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March 10, 1964 MASAMITSU NAGANO ETAL 3,124,415

POLYVINYL ALCOHOL FIBERS HAVING HIGH CRYSTALLINITY AND KNOT STRENGTHFiled Sept. 2 1960 5 HOURS 3 HOURS I HOUR 2 OJOU m0 uummvuc TEMPERATUREINVENTORS MASAMITSU NAGANO BYHIDEO TOKUMITSU ATTORNEY United States.Patent 3 124 415 PGLYVINY L ALCQI-IbL FIBERS HAVING HIGH CRYSTALLY ANDKNOT STRENGTH v Masamitsn Nagano and HideoTolrnmitsn, ()kayama City,

Japan, assignors to Knrashiki Rayon C0,, Ltd, Kuraslriki-shi, .lapan, acorporation of Japan Filed Sept. 2, 1960, Ser. No. 53,671

1 Claim. (Cl. 8-1301) This invention relates to the treatment ofpolyvinyl alcohol fibers and is more particularly concerned with theheat-treatment of such fibers.

Heat-treatment of polyvinyl alcohol fibers is carried out to increasethe crystallization of the molecules of polyvinyl alcohol and to promotethe water-resistance and elasticity of the fibers. However, inaccordance with the conventional heat-treating method. The fibers areheated only at a temperature above the second transition point for aspecified time and no consideration is given to the speed of cooling ofthe fibers after the heat treatment.

The mechanical properties of polyvinyl alcohol fibers will be influencedby the size and number of crystalline particles in the fibers.particles, the higher the strength and water-resistance of the fibers.When polyvinyl alcohol fibers are to be used for making fishing nets andthe. like, wherein fibers of a high knot strength are required, it isnecessary to provide fibers of large crystalline particles. However,there is danger that the fibers will harden. Accordingly, problems arepresent in the production of polyvinyl alcohol fibers having desiredcharacteristics of the type indicated which are not solvedby'conventional heat-treating operations.

It is an object of the present invention to provide a process ofheat-treating polyvinyl alcohol fibers to impart to them a highpercentagecrystallinity in the form of large crystal particles and highknot strength.

In accordance with the present invention, polyvinyl alcohol fibers arefirst heat-treated only for a short time at a temperature above thesecond transition point but below the melting point, e.g. at 200 to 225C., in accordance with known practice, and thefibers are then cooledunder controlled temperature and time conditions. When the time ofcooling is long, the crystallinity will be increased but a portion ofthe polyvinyl alcohol molecules will be thermally decomposed andsaturated or unsaturated carbonyl radicals will be produced and'discoloration will occur. In accordance with the invention,discoloration is prevented, and crystallinity and knot strength areincreased, by slowly cooling the fibers by maintaining them at atemperature above the second transition point (85 Q), but not above 100C., for a period of time up to two hours, preferably /z to 2 hours, andthen allowing them to cool at room temperature, i.e. about 25 C. untilthey are at room tempera-' ture. During the heatetreatment and duringthe controlled'cooling of the process of this invention, the fibers aremaintained at constant length until left at room temperature.

The invention will be further understood by reference heated byimmersion in a molten metal (lead) bath at 220 C. for 1.5 minutes andwere then cooled by the following procedures, while under tension tomaintain constant length.

Sample No. 1: In substantially saturated Na SO solu- Thus, the largerthe crystalline tion (as used for wet spinning) at 30 C. for 5 minutes,then left at room temperature.

Sample No. 2: In substantially saturated Na SO solution at 10 C. for 5minutes, then left at room temperature.

Sample No. 3: In an oven at 110 C. for 10 minutes, then left at roomtemperature.

Sample No. 4: In an oven at 110 C. for 1 minute, then left at roomtemperature.

Sample No. 5: Immediately left at room temperature.

Sample No. 6: Immersed for 1 minute in a mixture of solid carbon dioxideand acetone, then left at room temperature.

When the mechanical properties and the percentage crystallinity of thefibers treated as described above were determined, the values set forthin Table 1 were obtained:

Table 1 Softening point in water Dry strength a s! denier) PercentageCrystallinity Fineness (denier) Four samples of wet-spun polyvinylalcohol fibers were heated by immersion in a molten metal (lead) bath at225 C. for 1.5 minutes and were then cooled at various temperatures asdescribed below.

Sample No. 1: In an oven at 100 C. for 1 hour, then left at roomtemperature.

Sample No. 2: In an oven at C. for 1 hour, then left at roomtemperature.

7 Sample No. 3: In an oven at 60 C. for 1 hour, then left at roomtemperature. Sample No. 4: Left at room temperature immediately.

The properties of the thus-treated fibers were found to be as follows:

' Table 2 Wet Wet knot Softening Sample No. Fmeness strength strengthpoint in (denier) (granis/ (grams/ Water denier) denier) 0) These testsshow that slow cooling at a temperature above the second transitionpoint C.) is effective to increase the wet knot strength and otherproperties.

EXAMPLE 3 Five samples of wet-spun polyvinyl alcohol fibers wereheat-treated at. 225 C. for 15 minutes as described in Example 2 andthey were then further treated at 100 C. for various periods of time asdescribed below.

Sample No. 1: Maintained in an oven at 100 C. for 2 hours, then left atroom temperature.

The results of tests upon the thus-treated fibers are set forth in thefollowing table:

Table 3 Wet Wet knot Fineness strength strength Sample N o. (diener)(grams/ (grams/ denier) denier) These results show that it is desirableto effect slow cooling as a type of annealing for a prolonged period oftime. However, the relationship between the degree of discoloration ofthe fibers and the annealing time and temperature are shown in theaccompanying drawing. At temperatures of up to about 100 C., even whenthe fibers were treated for hours, there was no discoloration.

As previously indicated, the process of this invention is applicable toall types of fibers derived from polyvinyl alcohol produced inconventional manner and subjected to conventional treatments andprocessing operations, such as acetalization, stretching, and the like.Such fibers are conventionally spun from spinning solutions by known wetand dry spinning techniques. Spinning techniques are described, forexample, in Cline et al. US. Patent 2,610,360 and Osugi et a1. Patent2,906,594. An especially preferred spinning technique is described incopending As previously mentioned, the heat treating step which iscombined with the controlled cooling step of this invention is carriedout in conventional manner at a temperature above the second transitionpoint but below the melting point, e.g. at 200 to 225 C., for a shorttime, e.g. 1 to 2 minutes. Heat treatment is effected in a molten metalbath or in a hot salt bath or even in heated air in accordance withknown practice. Such heat treatment, and subsequent controlled cooling,is effected while maintaining the fibers under tension at a constantlength in accordance with conventional techniques.

It will be understood that the conditions and the relative relationshipsset forthabov e which are illustrative of the invention are thosepreferred in carrying'out the process of the invention but it will beunderstood that other conditions and relationships may be used withinthe scope of the invention.

It will, therefore, be further understood that various changes andmodifications may be made in the embodiments of the invention hereindescribed without departing from the scope of the invention as definedin the appended claim. It is intended, therefore, that all mattercontained in the foregoing description and in the drawing shall beinterpreted as illustrative only and not as limitative of the invention.

We claim:

Polyvinyl alcohol fibers having a high percentage of crystallinity and ahigh knot strength produced by heating polyvinyl alcohol fibers to atemperature above the second application Serial No. 336,166 of Tomonariet al., filed February 10, 1953. Typical processes of treatingpolypatents and applications.

transition point but below the melting point and effecting step-Wisecooling of said fibers by maintaining them at a temperature above thesecond transition point but at a maximum of about C. for a period oftime up to 2 hours and then cooling the fibers to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS2,514,088 Pinsky July 4, 1950 2,732,592 Tunnicliif et a1. Jan. 31, 19562,878,519 Wolinski Mar. 24, 1959 2,906,594 Osugi Sept. 29, 1959

